Minimization of Background for HPGe using Passive Shielding

Unnati Gupta* , Arpita Datta and Alpana Goel Amity Institute of Nuclear Science & Technology, Amity University Uttar Pradesh, Noida - 201313, INDIA * email: ugupta@amity.edu Abstract Minimization of background plays a very important role in various studies based on acquiring gamma ray spectrum by the HPGe detectors in indoor research-laboratories. In comparison of outdoor labs , indoor laboratories have higher background level. In such laboratories, the natural background sources around the detector are building material, terrestrial radiation eg, 40K and decay products[1-4] of Uranium and Thorium. Moreover, indoor air radioactivity, cosmic radiation, ancillary equipment and other radioactive samples nearby the detection system are also prominent sources of background radiation. Keep in mind the minimization of above background radiations, to enhance the activity subsequently reduction in Compton continuum, a simple and economical passive graded shielding containing the layers of Copper, lead, Tin, Mild Steel and coating of Epoxy paint has been designed, which is a combination of low and high Z materials. Further, the shielding material itself is also the prominent source of ?, ? and γ radiations. The reduction of these radiations has also been considered in the present design. To reduce the air radioactivity 222Rn, a provision of vacuum pump has been made. During the design, the gamma rays of energies, 65.3 keV (shield material), 75 to 85 keV( X-rays of lead), 1460 keV (40K) and beta rays of 1696 keV( shield material) are examine, and interaction probabilities and absorption coefficient for shield material are taken from the refence [5] . The present design of passive grade shielding will reduce upto ~0.001 %. background intensities. References: [1] M.Tufail, Nasim Akhtar and M.Waqas, Radiation Measurements, Volume 41 (2006) 443-451 [2] Prateek Arora et al., Proceedings DAE-BRNS Symposium Vol 63(2018), 316 [3] P. Bossew, Elsevier Publication; A very long-term HPGe-background gamma spectrum doi:10.1016/j.apradiso.2004.09.006 [4] G.F. Knoll, (1989) Radiation Detection and Measurement. John Wiley & Sons, Inc., New York. [5] John H. Hubbell, NSRDS-NBS 29, 85 (1969).